Effect of microcracking on the micromechanics of fatigue crack growth in austempered ductile iron

The effect of microcracking on the mechanics of fatigue crack growth in aus tempered ductile iron is studied in this paper. The mechanism of fatigue cr ack growth is modelled using the boundary element method, customized for th e accurate evaluation of the interaction effects between cracks and microcr acks emanating from graphite nodules. The effects of nodule size and distri bution and crack closure are considered, with deviation bounds of computed results estimated through weight-function analyses. A continuum approach is employed as a means of quantifying the shielding effect of microcracking o n the dominant propagating crack, due to the reduction of stiffness of the material in the neighbourhood of the crack tip. Although the results obtain ed may not yield actual numbers for real cases, they are in accordance with experimental observations and demonstrate how the main factors affect the crack growth of the macrocrack.